1. Field of the Invention
The present invention relates to the field of processes for the preparation of alkanoic acids and alkanoic acid esters and, more particularly, to the preparation of such acids and esters from the catalyzed reaction of olefin, carbon monoxide and water and/or alkanol (a type of carbonylation reaction).
2. Description of the Prior Art
It is known from U.S. Pat. No. 3,952,034 to react an olefin or acetylene, carbon monoxide and water or alkanol in the presence of a soluble, i.e., homogeneous, catalyst system containing a polynuclear complex of palladium and iron or metal of Groups IVA, VA or IIIB, or a mixture of a soluble palladium salt and metal halide, to provide a carboxylic acid or ester. A similar reaction is described in German Patent No. 27 39 096 which also employs a soluble palladium compound or complex in combination with an aryl arsine as catalyst. Still other soluble palladium-containing catalysts for the aforedescribed carbonylation reaction are disclosed in U.S. Pat. Nos. 3,641,074; 3,816,490; 3,859;319; 3,919,272; 3,892,788; 3,917,677; 3,965,132; 3,968,133; and 3,987,089. While U.S. Pat. No. 3,887,595 describes the use of zero-valent palladium metal as a component of the carbonylation catalyst system, the result of the reaction is to provide a high ratio of straight-chain to branch-chain carboxylic acids and esters. For some important industrial applications, for example, monomer precursors or lubricants, it is highly desirable to provide a reaction product which is exclusively made up of branched product or a product in which the branched product at least predominates. Although some of the fully soluble catalyst systems heretofore known in the carbonylation of alkenes and alkynes may be effective for providing relatively high ratios of branched carboxylic acids and esters in relation to the quantities of straight-chain product produced, nevertheless they are at an operational disadvantage compared to the insoluble, i.e., heterogenous, catalyst systems since the solubility of the former complicates product separation and recovery procedures.
Accordingly, there has heretofore existed a need for an effective heterogenous catalyst system for the reaction of olefin, carbon monoxide and water and/or alkanol to provide predominantly alpha-methyl monoalkanoic acid and/or ester.